Aspects of the present invention relate to a liquid transport apparatus which transports a liquid.
In a printer which records an image or the like by discharging ink onto a recording medium, such as a recording sheet, an ink-jet recording head which ejects ink from nozzles toward the recording medium is generally employed. However, in such an ink-jet recording head, the structure of a flow passage for generating ink ejection pressure and the structure of an actuator are special and complicated. As a result, there is a limitation in reducing the size of the recording head by arranging nozzles in a high density relationship.
Accordingly, a recording head of a new type has been proposed using an electrowetting phenomenon in which, when an electrode potential is changed in a state where the surface of an electrode is covered with an insulating layer, the liquid repellency (wetting angle) at the surface of the insulating layer changes . The recording head includes individual flow passages each composed of a recess. An individual electrode is provided on each individual flow passage (on the bottom face of the recess), and the surface of the individual electrode is covered with an insulating layer. Ink disposed in the head is in contact with a common electrode which is maintained at ground potential, and the electric potential of the ink is always set at ground potential. A pump, which pressurizes the ink toward a discharge port located at the end of the individual flow passage, is also provided on the upstream side of the individual flow passage.
When the electric potential of the individual electrode is set at the ground potential and there is no electrical potential difference between the ink and the individual electrode, the liquid repellency (wetting angle) at the surface of the insulating layer interposed between the ink and the individual electrode becomes high when compared with a region of the bottom face of the recess not provided with the insulating layer. Consequently, the ink is not allowed to pass over the surface of the insulating layer and flow toward the discharge port, and the ink is not discharged from the discharge port. On the other hand, when the electrical potential of the individual electrode is switched to a predetermined electrical potential that is different from the ground potential, an electrical potential difference occurs between the ink and the individual electrode. As a result, the liquid repellency (wetting angle) at the surface of the insulating layer interposed between the ink and the individual electrode is decreased causing the electrowetting phenomenon. Consequently, the ink pressurized by the pump is allowed to wet the surface of the insulating layer and move toward the discharge port, and the ink is discharged from the discharge port.